Study Guide Exam 2 Lab PDF

UNIT LAB 2 LM 16 CONTROL OF GROWTH WITH HEAT: 1. How heat damages microbes: Heat works by denaturing proteins and disrupting the cell membranes and enzymes of microbes which are essential for their survival. As proteins unfold, the microbe loses its ability to function leading to cell...

UNIT LAB 2 LM 16 CONTROL OF GROWTH WITH HEAT: 1. How heat damages microbes: Heat works by denaturing proteins and disrupting the cell membranes and enzymes of microbes which are essential for their survival. As proteins unfold, the microbe loses its ability to function leading to cell death. 2. Compare and contrast use and effectiveness of using dry vs moist heat for disinfection: Moist heat Dry heat Examples Boiling, autoclaving, Flaming, baking pasteurization Effectiveness Moist heat is more effective Dry heat is less effective and than dry heat because water requires higher temperature conducts heat better than air for longer periods to achieve and penetrates cells more sterilization efficiently Mechanism It kills microbes by Kills by oxidizing cell coagulating their proteins. components and denaturing For example, autoclaving proteins, but slower than can kill resistant forms like moist heat spores Common uses Sterilizing surgical Sterilizing glassware and instruments and media in metal instruments that might labs be damaged by moisture 3. Describe a structure some bacteria have to help resist extreme temperatures: ▪ Some bacteria form endospores which are highly resistant to extreme temperatures, desiccation, chemicals, and radiation. ▪ Endospores allow the bacteria to survive in harsh environments until conditions become favorable again. 4. Define thermal death rate (TDR), thermal death time (TDT) and decimal reduction time (DRT) ▪ TDR – the rate at which bacteria are killed at a particular temperature ▪ TDT – the shortest time required to kill microbes in a sample at a specific temperature ▪ DRT or D-value – time required to kill 90% of the microbes at a specific temperature How did we determine the TDT in out lab? ▪ In the lab we used different water temperatures to observe how long it took for bacteria to be completely killed. The setup included a water bath rack at varying temperatures, an oven set at 100℃, and a glass beaker of water on a hot plate. By placing samples of bacteria in each setup and checking at time intervals, we measured how long it took for all bacteria to be killed at each specific temperature allowing us to determine the TDT for each condition. How is DRT used to evaluate the effectiveness of a given heat treatment? ▪ The DRT measures how long it takes to reduce the microbial population by 90% at a specific temperature. By knowing the DRT, we can evaluate how effective the heat treatment is and how long it needs to be applied to ensure that the microbial population LM 17 CONTROL OF GROWTH WITH UV: 1. How does UV light damage cells? Specifically – what type of mutations do they cause? ▪ UV light primarily damages cells by causing mutations in their DNA. Specifically, UV light leads to the formation of thymine dimers – a type of mutation where two adjacent thymine bases on the same strand of DNA bond together disrupting normal DNA replication and transcription. If left unrepaired, these mutations can lead to cell death or malfunction. 2. What is minimum lethal dose?  ▪ The minimum lethal dose is the smallest dose of a harmful agent, such as UV light that is sufficient to kill a particular organism or population of cells. In this case it refers to the minimum amount of UV exposure required to kill cells in a sample. 3. How did we determine the UV minimum lethal dose in lab? ▪ In the lab, we exposed two different bacterial species to varying doses of UV light. We used different exposure times to observe the effect of UV light on cell survival. By increasing the exposure times for each bacterial species, we monitored the bacterial growth and determined the minimum lethal dose – the lowest amount of UV exposure needed to kill all the cells in the sample for each species. This helped us understand the sensitivity of each bacterial species to the UV light. 4. What structure might help bacteria resist high doses of UV light? ▪ Some bacteria such as endospore-forming bacteria (ex., Bacillus and Clostridium species) can resist high doses of UV light. Endospores have a tough outer coating and specialized DNA- repair mechanism that allow them to survive extreme conditions including UV radiation. Additionally, some bacteria possess DNA repair enzymes such as photolyases which can repair the thymine dimers caused by UV exposure, helping them recover from DNA damage.